In the technical field of mobile communications, various mobile communication systems in current use or for future use are developed by 3GPP (The 3rd Generation Partnership Project). In particular, an E-UTRA (Evolved UMTS Terrestrial Radio Access) system or an E-UTRAN (Evolved UMTS Terrestrial Radio Access Network) system is under discussion as a successor to a UTRA (UMTS Terrestrial Radio Access) system or a UTRAN (UMTS Terrestrial Radio Access Network) system which is based on a W-CDMA (Wideband-Code Division Multiple Access) system. The E-UTRA system or the E-UTRAN system is also referred to as “LTE (Long Term Evolution)”.
According to the 3GPP specification (see 3GPP TS36.401 V8.8.0 (2010 June)), an interface between a radio control base station (eNB: evolved Node B) and a switching center (MME: Mobile Management Entity) in the LTE system is arranged as a multi-connection configuration in which a plurality of eNBs and a plurality of MMEs are mutually connected, thereby achieving load distribution. Upon connection establishment, capacity information indicating the number of calls that the MME can accept is transmitted from the MME to the eNB (see 3GPP TS36.413 V8.10.0 (2010 June)). The eNB identifies a connection-target MME (an MME to which a call is to be connected) based on information included in a radio connection request (Message 3) or a radio connection complete report (Message 5) from a mobile station (UE: User Equipment). If the eNB cannot identify a connection-target MME, the eNB selects an MME based on capacity information which has been transmitted from the MMEs.